Guanine nucleotide-binding proteins, otherwise known as G proteins, are involved in transmitting chemical signals from outside the cell to inside the cell by way of triggering a series of biochemical reactions which ultimately effect physiological changes within the cell. G protein-coupled receptors are transmembrane receptors that sense molecules outside the cell and activate signal transduction pathways and intracellular responses. It is well known that G protein-coupled receptors are involved in regulating many diseases.
Type 1 and type 2 cannabinoid receptors, hereinafter CB1 and CB2, are G protein-coupled receptors found in mammal tissues. CB1 receptors are expressed mainly by neurons of the central and peripheral nervous system, whereas the CB2 receptors occur centrally and peripherally particularly in immune cells. Signal molecules may bind to the two cannabinoid receptors outside the cell, causing a cascade of biochemical reactions within the cell. For example, CB1 receptors coupled through G proteins inhibit adenylyl cyclase and activate mitogen-activated protein (MAP) kinase. In addition, CB1 receptors inhibit presynaptic N- and P/Q-type calcium channels and activate inwardly rectifying potassium channels. The combined effect of these biochemical changes generates a variety of physiological effects, of which many are still to be discovered.
The discovery that mammal tissues express cannabinoid receptors was accompanied by the discovery of endogenous ligands to these receptors called endocannabinoids, which along with CB1 and CB2 constitute the endocannabinoid system. It was discovered that certain disorders cause the levels of endocannabinoids, the density of the cannabinoid receptors and the efficiency of the coupling of the cannabinoid receptors to increase. It has been noted that this upregulation of the endocannabinoid system often suppresses undesirable symptoms and signals, suggesting that the endocannabinoid system is autoregulatory.
In order to better understand the endocannabinoid system, researchers have been developing antagonists and inverse agonists with specificity for either CB1 or CB2. Antagonists are receptor ligands that do not provoke a biological response upon binding to a receptor but block or weaken an agonist-mediated response. Inverse agonists on the other hand bind to the same receptor as an agonist and reverse the activity of receptors, or in other words, exert an opposite pharmacological effect of a receptor agonist.
The discovery of antagonists and inverse agonists of CB1 or CB2 receptors is extremely important in the field of medicine as there are many significant physiological and pathophysiological conditions in which the endocannabinoid system has been demonstrated to play a role. These include diseases of the central nervous system such as Parkinson's, Alzheimer's, and depression, as well as diseases of the peripheral nervous system, such as inflammatory and neuropathic pain, obesity and other alimentary disorders.
Incidentally, there are several published accounts documenting the importance of antagonists or inverse agonists of either CB1 or CB2 receptors in the prophylactic or combative treatment of the aforementioned diseases. For example, WO/2006/119260 refers to a pharmaceutical composition of an antagonist of the CB1 receptor in association with a microsomal triglyceride transfer protein inhibitor which acts in the intestine to treat obesity or alimentary disorders. WO/2006/100205 refers to new cannabinoid receptor modulators and their use to treat diseases such as pain, neurodegenerative disorders and alimentary disorders. US/2005/101542 refers to yet another pharmaceutical composition comprising cannabinoid receptor antagonists that combined with another protein agonist can reduce the consumption of foods, alcohol, or other appetizing substances. Finally, Brazilian patent application PI0114410-3 refers to the pharmaceutical combination of the antagonist of CB1 and the appetite suppressant sibutramine that is useful in the treatment of obesity.
One underlying feature of these published accounts is that they demonstrate how an antagonist or inverse agonist of CB1 may treat obesity. CB1 receptors are targets for treating obesity because they are highly expressed in hypothalamic areas which are involved in central food intake control and feeding behavior. These regions are also interconnected with the mesolimbic dopamine pathway, the so-called “reward” system. Furthermore, peripheral CB1 receptors are located in the gastrointestinal tract, liver and in adipose tissue. These combined facts strongly indicate that the endocannabinoid system may be directly involved in feeding regulation, fat control and blood glucose regulation. For example, it is known in the literature that the administration of exogenous CB1 agonists such as Δ9-tetrahydrocannabinol (THC), the active ingredient of Cannabis sativa, increases food intake by increasing motivational rewards. Antagonism of CB1 could potentially inverse these effects by inhibiting the dopamine-mediated rewarding properties of food and by inversing the process for storage of fats.
Obesity is now the most common nutritional disorder in industrialized countries. Defined as a body mass index of greater than 30, obesity arises from the accumulation of excess fat in the body from over consumption of fatty foods. Prevalence of obesity in the US and Europe has reached epidemic levels. Data from the World Health Organization Multinational MONICA (MONitoring of trends and determinants in CArdiovascular diseases) project shows that in some parts of Europe over 70% of men aged 55-64 years are clinically obese or overweight and almost 70% of women in this age group. Furthermore, one in five of all Americans are obese and one in three overweight. In addition, increasing rates of childhood obesity are likely to exacerbate the trend towards increasing obesity in adulthood.
In addition, research indicates that obese individuals are predisposed to insulin resistance and diabetes. (see Boden, Free fatty acids, a link between obesity and insulin resistance, 3 Front. Biosci. 169-75 (1998)). Insulin resistance is a term referring to the condition when one's cells have become less sensitive to the effects of insulin in balancing blood glucose levels. Insulin is the hormone secreted by the pancreas which helps glucose to enter cells where it is turned into energy. Obese individuals have high levels of free fatty acids in their blood plasma. Free fatty acids lead to increased insulin resistance because they compete with and inhibit insulin from stimulating glucose uptake, thus leading to increased and potentially life threatening blood glucose levels. Hence, decreasing the amount of free fatty acids and increasing insulin sensitivity is central to the prevention and treatment of diabetes.
People that experience insulin resistance provoke the pancreas to work harder and release increasing amounts of insulin to achieve a healthy blood glucose balance. This can lead to two major problems. First, the pancreas may become exhausted and insulin production may therefore slow down to abnormally low levels. This would trigger adult onset type II diabetes by increasing blood glucose levels. A second potential problem may be that the insulin resistant patient does not develop diabetes but may suffer from abnormally high levels of insulin in the blood which can cause chronic obesity, high blood pressure, heart disease and possibly some cancers.
There are no prior art documents suggesting a pharmaceutical composition of hemopressin, a mimic, derivative or fragment thereof to treat diabetes.
A synthetic compound, rimonabant (SR141716A), has however been demonstrated to behave as an inverse agonist at the CB1 receptor and achieve weight-reducing effects over extended periods in rodents and humans (see Van Gaal et al., Effects of the cannabinoid-1 receptor blocker rimonabant on weight reduction and cardiovascular risk factors in overweight patients, 365 Lancet 1389-1397 (2005)). The action of rimonabant is limited however as the United States Food and Drug Administration rejected rimonabant because clinical trials suggested a higher incidence of depression, anxiety, and suicidality following prolonged administration (see R. Christensen et al., Efficacy and safety of the weight-loss drug rimonabant, 370 Lancet 1706-1713 (2007)). Current research efforts are therefore underway to find safer compounds that behave as selective antagonists or inverse agonists of the CB1 receptor.
The peptide hemopressin may be a safer alternative compound that exhibits selectivity for CB1. Hemopressin is a product of the hemoglobin a chain, discovered in rat brain homogenates. Further studies have indicated that peptides containing the hemopressin amino acid sequence are generated in vivo, suggesting indeed that hemopressin may be a safer alternative than rimonabant or other synthetic inverse agonists or antagonists of CB1, because of its potential endogenous presence.
Hemopressin was initially found by Dale et al. to have nonopioid antinociceptive effects (see Antinociceptive action of hemopressin in experimental hyperalgesia, 25 Peptides 431-436 (2005)). Further studies demonstrated that the peptide hemopressin acts specifically on the cannabinoid system as a CB1 receptor inverse agonist and can interact with both peripheral and central pain pathways in vivo (see Heimann et al., Hemopressin is an inverse agonist of CB1 cannabinoid receptors, 104 PNAS 20588-593 (2007)). This article also demonstrated how hemopressin is effective in treating hyperalgesia when administered locally or systemically. Furthermore, this article suggested that based on hemopressin's specificity for CB1 it may have an effect on body weight and food intake in the same way as rimonabant.
A recent article, published in the Journal of Neuroscience on May 26, 2010 by Garron T. Dodd et al., titled The peptide hemopressin acts through CB1 cannabinoid receptors to reduce food intake in rats and mice, demonstrates how hemopressin acts as an inverse agonist on CB1 receptors and modulates the activity of appetite pathways in the brain in a manner contrary to how THC, and other CB1 agonists, modulate appetite pathways in the brain. More specifically, Dodd shows that hemopressin can: 1) antagonize CB1 agonist-induced internalization of the CB1 receptor in vitro; 2) induce hypophagia in vivo when administered centrally; 3) induce hypophagia in vivo when administered systemically; 4) overcome powerful orexigenic drives in fasted or obese mice; and 5) reduce feeding in a behaviorally specific manner.